Hacked iPhone 4 to allow 'Stereo' HD video recording

Discussion in 'Jailbreaks and iOS Hacks' started by A4Mania, Oct 1, 2010.

  1. A4Mania macrumors newbie

    Joined:
    Oct 1, 2010
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    Canada
    #1
    Apparently, the dual-mic setup on the iPhone 4 can be optimized either in future iOS updates or(if you can't wait) hacked on jailbroken devices to record stereo audio tracks. At the moment, the secondary mic(for noise cancellation) at the top of the phone is used by the Camera app for recording audio/video while the primary mic at the bottom of the device is used for voice calls & facetime. However, as of iOS 4.1(latest version), both mic cannot be used to 'record' audio at the same time. A system filter algorithm at the root level ensures that sounds are pre-filtered when both mic are in use at the same time such that the full spectrum audio from either mic are not outputed for use at the developer level, but that's not to say it can't happen! Jailbreakers twinkering with iOS 4.0.1 is trying to find a way to bypass the filtering algorithm therefore allowing full spectrum audio output from both microphones despite rumors that the algorithm is hardcoded into the Apple audio chipsets instead of the operating system platform itself. So far, they've been marginally successful by modifying the I/O device control codings to allow simultaneous data feeds from both mics. There's however still some bugs that needed to work through for this to work.
     
  2. thelatinist macrumors 603

    thelatinist

    Joined:
    Aug 15, 2009
    Location:
    Connecticut, USA
    #2
    I imagine that the mics are not identical, and with their disparate placement and directionality it's going to be almost impossible to balance the audio. Why not just record in mono and convert to joint stereo? I bet that'd be much better quality than trying to futz with mics that aren't designed to work together.
     
  3. sidewinder macrumors 68020

    sidewinder

    Joined:
    Dec 10, 2008
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    #3
    Not to mention that it's hard to get a reasonable stereo recording with mics that are 5 inches apart.

    S-
     
  4. thelatinist macrumors 603

    thelatinist

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    Location:
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    #4
    Indeed. You're going to have almost no separation, and any benefit would be far outweighed by the lack of balance, etc.
     
  5. A4Mania thread starter macrumors newbie

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    Oct 1, 2010
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    Canada
    #5

    Recording in mono then post-converting to stereo is not true stereo, it'd be like plugging your right ear and imagining you're hearing the sound through both ears, there'll be no directional variation, no spatial space, just still mono and the quality will be inferior on the contrary.
    The manufacturer of the two mics on the handset are indeed different(top one is by Infineon, bottom is by Knowles) but their designs are very similar and they both serves the same purpose, to record soundwaves. Any variations in sensitivity, frequenzy response and synchronization can be easily calibrated in the audio post-processing. When it comes to distance between mics, the further apart they are(within range) on the same plane the more accurate the stereo reproduction would be and the more spartialization you get. The mics on the iPhone 4 are almost perfectly placed for recording in stereo(on each side-L/R; of the phone pointing in opposite direction on one plane) when shooting video in landscape mode, exactly same reason why Apple desided to use this setup for voice quality enhancement. They ARE designed to work together in order for noise cancellation to be effective.
     
  6. thelatinist macrumors 603

    thelatinist

    Joined:
    Aug 15, 2009
    Location:
    Connecticut, USA
    #6
    I thought it was pretty clear from my comments that I understood the difference. I've heard many very good mono recordings, and I've heard some really horrific stereo recordings. My point is that you are not going to get what you want out of these microphones, with their very different characteristics and excessive directionality. I'll take a mono recording any day over the kind of stereo recording you'll get out of this hack.

    Oh, thank you for defining microphone for me. I didn't know what these strange 'microphone' things did. :rolleyes:

    I think you're kidding yourself if you believe that a microphone designed to pick up and cancel out background noise and a microphone designed to pick up voices and filter out background noise can be made to record acceptibly balanced stereo audio channels in real-time post-processing on the iPhone (not to mention that you're going to have to build such post-processing into a completely new video recording app).
     
  7. touchmonkey macrumors 6502

    Joined:
    Oct 14, 2008
    #7
    I'm in the midst of trying to record in stereo on the "i's".
    I have been able to do so (in true stereo) on my 3g and Classic, with the right hardware. Not Nano, iPad, or iP4.
    (I could rule the world if I could only get the parts.)
    This is a big fail of Apple (imho) to not allow stereo recording through the headset jack.
    Would be simple (? I always reserve the right to be completely wrong) to do, and the devices are more than capable.
    And it would rock.
    (Don't yell at me.)
     

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